1. Field of the Invention
The present invention relates to circuit breakers and, more specifically, to an operating mechanism having pivoting cradle and a metal pivot structure upon which the cradle pivots.
2. Background Information
Circuit breakers having an operating mechanism and trip means, such as a thermal trip assembly and/or magnetic trip assembly, which are automatically releasable to effect tripping operations and manually resettable following tripping operations are known in the art. An example of such circuit breakers is disclosed in U.S. Pat. No. 5,805,038 which is assigned to the assignee of this application and which is incorporated by reference. Such circuit breakers, commonly referred to as “miniature circuit breakers,” have been in use for many years and their design has been refined to provide an effective, reliable circuit breaker which can be easily and economically manufactured on a large scale. As such, the ease of manufacture of such circuit breakers is of importance.
Circuit breakers of this type include at least one set of separable contacts disposed within a non-conductive housing. Typically, there is a fixed contact attached to the housing and a movable contact coupled to an operating mechanism. The operating mechanism includes a movable handle that extends outside of the housing. The handle has essentially three stable positions: on, off, and tripped. These three positions tell the operator what condition the contacts are in when the handle is viewed. Thus, when the contacts are in a first, closed position, the handle is maintained in the on position. The operating mechanism may be actuated to move the contacts into a second, open position. From the first, closed position, once the trip means is automatically released so as to protect electrical circuitry from damage due to an overcurrent condition such as an overload or relatively high level short circuit, the contacts separate and the handle automatically moves to the tripped position which is located between the on position and the off position. The circuit breaker must then be reset, as is known in the art, by moving the handle beyond the off position to a reset position from which the handle returns to the off position when released. The circuit breaker may then be manually operated from the off to on position in order to return the contacts to the first, closed position and allow the circuit breaker to resume normal operation.
Movement of the contacts is accomplished by an operating mechanism. The operating mechanism typically includes components such as the previously mentioned handle, an operating arm, upon which the movable contact is disposed, and a trip device, such as the previously mentioned thermal trip assembly and/or magnetic trip assembly as well as a cradle. The cradle is coupled to a spring and disposed between the trip device and the operating arm. The components may further include a frame to which the other components are coupled. The operating mechanism is disposed within an operating mechanism cavity within the circuit breaker housing. In the prior art, selected components, such as the handle and the cradle, were mounted on, and structured to pivot about, protrusions within the operating mechanism cavity. Thus, the operating mechanism needed to be assembled within the operating mechanism cavity. This assembly procedure is time consuming as it must be performed within the enclosed operating mechanism cavity. Additionally, the operation of the operating mechanism, which is generally made of steel, would slowly degrade the housing as the components pivoted against the softer, typically plastic, housing material.
There is, therefore, a need for an operating mechanism for a circuit breaker which has components that do not pivot about the soft housing material.
There is a further need for an operating mechanism for a circuit breaker with a metal pivot structure about which the operating mechanism components, such as the cradle, may pivot.